Ammonium nitrate explosive composition

ABSTRACT

An explosive composition is provided which contains particulate ammonium nitrate, particulate metal and an aqueous phase saturated with ammonium nitrate.

United States Patent [72] inventors Joseph R. I-Iradel Mount Pleasant, Mich.;

Harold E. Staadt, Tulsa, Okla.

Apr. 21, 1969 Nov. 16, 1971 The Dow Chemical Company Midland, Mich.

Original application Jan. 5, 1959, Ser. No. 784,881. Divided and this application Apr. 21, 1969, Ser. No. 818,088

[21] App]. No. [22] Filed [45] Patented [73] Assignee [54] AMMONIUM NITRATE EXPLOSIVE COMPOSITION 16 Claims, No Drawings 1521 u.s.c1 149 21, 149/43, 149/44, 149/60, 149/112. 149/114 511 1111.01 C06bl/04 [50] Field of Search 149/2l,43, 44, 60, 112, 114

[56] References Cited UNITED STATES PATENTS Re 26,325 12/1967 Hradei et a1. 149/21 X 2,836,484 5/1958 Streng et a1... 149/21 X 3,091,559 5/1963 Staadt 149/60 X 3,094,443 6/1963 Hradel et a1. 149/21 X 3,094,069 6/1963 i'lradel et a1.. 149/21 X 3,121,036 2/1964 Cook et al. 149/21 Primary Examiner-Benjamin R. Padgett Assistant Examiner-Stephen .1. Lechert, Jr.

Allorneys-Griswold & Burdick, Bruce M. Kanuch and William R. Norris ABSTRACT: An explosive composition is provided which contains particulate ammonium nitrate, particulate metal and an aqueous phase saturated with ammonium nitrate.

AMMONIUM NITRATE EXPLOSIV E COMPOSITION This is a division of application, Ser. No. 784,881, filed Jan. 5, 1959.

it has been a desideratum in the explosives art to formulate and compound explosive compositions which are easily and safely loaded in a borehole or fissure in a earth formation which are of relatively low cost and which do not produce toxic substances on detonation.

Accordingly, it is an object of this invention to provide an ammonium nitrate explosive mixture in the form of an aqueous composition which may be readily loaded as by pumping the composition into a borehole or by first placing the composition, if pasty, in rigid or flexible containers and positioning the containers in a borehole, the aqueous composition having substantially no voids therein and especially when in the form of a slurry the composition further filling any confining space in the manner of a liquid so as to generally eliminate voids below the surface of the slurry.

it is another object of the invention to provide an ammonium nitrate explosive composition which can be prepared from low-cost materials.

it is another object of the invention to provide an ammonium nitrate explosive composition compounded from substances which do not produce toxic products when the composition is detonated.

it is a further object of the invention to provide an ammoniurn nitrate explosive composition which is readily compounded at or near the site where it is used.

These and other objects are attaining upon admixing ammonium nitrate and water in suitable proportions, hereinafter, described, whereby there is obtained a paste or slurry of particulated ammonium nitrate in its saturated aqueous solution.

The compositions of the invention may be compounded by first preparing an aqueous solution of ammonium nitrate form water and any grade of ammonium nitrate such as fertilizer grade ammonium nitrate or explosives grade ammonium nitrate, and slurrying therein or mixing therewith a particulated ammonium nitrate, However, a most economical procedure is that of admixing a particulated ammonium nitrate with one of the aqueous ammonium nitrate solutions of commerce such as an aqueous solution containing about 84 percent of ammonium nitrate as obtained in the manufacture ofammonium nitrate.

While a fine particulate grade of ammonium nitrate may be used to obtain a composition with somewhat greater work potential, it is generally more economical to use and inexpensive grade such as fertilizer grade ammonium nitrate in either prilled or granular form and, if necessary, to increase the size of the load slightly. However, though a relatively coarse grade of ammonium nitrate may be employed a grade of ammonium nitrate having more than about 5 percent of particles of a size greater than that passing about a lO-mesh sieve (US. Sieve Series) is to be avoided as decreasing the sensitivity of the composition to initiation to an undesirably low level.

The components of the inventions may be combined in proportions varying from about 75 to 97 percent by weight of ammonium nitrate and from about 3 to 25 percent by weight of water to produce a pasty to pumpable two-phase composition, one of the phases being solid ammonium nitrate, the other an aqueous solution saturated with respect to ammonium nitrate. it is to be understood that while compositions in this range will under room temperature conditions contain both dissolved ammonium nitrate and solid phase particulate ammonium nitrate, the relative amount of ammonium nitrate in each phase is determined by the temperature of the mixture under equilibrium conditions. At higher temperatures more solid particulate ammonium nitrate will be taken into solution than at lower temperatures.

While such an aqueous composition of ammonium nitrate explosive is detonable upon initiation by a suitably heavy initiator, it is generally to be preferred that the slurry be admixed with up to about 35 percent by weight of a sensitizer to increase sensitivity as well as work potential. In this instance the composition comprises up to 35 percent by weight of a sensitizer, 40-97 percent by weight of ammonium nitrate, a portion of which is in particulate form, and 3-25 percent by weight water containing dissolved ammonium nitrate. Suitable sensitizers include light metals such as magnesium and magnesium-base alloys comprising at least percent of magnesium, and aluminum and aluminum-base alloys, comprising at least 80 percent of aluminum, the light metal being in particulated form. Atomized pellets of light metal as well as the ground flake form of metal may be used in compounding the explosive composition of the invention. Examples of suitable magnesium-base alloys include those having the ASTM designations ZKlO, ZK60, A241, as well as AZlll containing 1 percent of manganese, ZK60 containing 2 percent of thorium, and an alloy containing 2.8 percent of aluminum, 8.4 percent of zinc, the balance magnesium. While the particulated metals may be used in the form of ground or flaked particles a desirable form is that of atomized pellets, for example, atomized metal pellets obtained as described in US. Pat. Nos. 2,699,576 and 2,728,107.

Ground metals as produced are generally quite varied in particle size and usually contain a substantial amount of fines passing a 325-mesh sieve. Not only are these fines rather easily ignited in air but they contribute to low-level initiation of particulate ammonium nitrate in admixture therewith. Such fines are thus unsuitable in one preparation of relatively insensitive ammonium nitrate explosive mixtures. Ground metals may be used upon separating the fines as by screening and selecting particles about percent of which are retained on a 140- mesh sieve and not more than 1 percent of which pass a 200- mesh sieve. It is also desirable to reject coarse metal particles not passing a 20-mesh sieve as these are too large to react effectively during the brief interval of the detonation reaction of ammonium nitrate, though the presence of a small percent of larger particles does not particularly adversely affect detonability of an ammonium explosive mixture.

On the other hand atomized metal pellets produced according to the US. patents referred to above are readily formed in a narrow range of particle sizes with little fines. While the same limits of metal particle sizes generally apply whether the metal is ground or pelletized the following is a sieve analysis of a suitable pelletized magnesium-base alloy having the ASTM designation ZK60.

Other suitable sensitizers for the present explosive composition include finely divided carbon, preferably passing a 325- mesh sieve, and mixtures of carbon and the above-mentioned particulate light metals. It is to be preferred that the carbonparticulate metal mixtures contain at least 50 to 75 percent by weight of the particulate metal.

Additional sensitizers which may be used include such inorganic salts as potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chromate, potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate and ammonium hypophosphite all of which contain nitrogen and exhibit a melting point or decomposition point above a temperature of C. These inorganic sensitizers are best employed in the explosive composition of the invention in the range of about 15 to 35 percent by weight of the total composition.

if desired the explosive composition of the invention may be thickened upon admixing therewith from about 0.1 to 5 percent based on the weight of the liquid phase, of a thickening agent such as methyl cellulose or gum karaya. Other suitable thickening agents are carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu natural, lrish moss, Iceland moss and high molecular weight polyacrylamide.

Compositions of the invention containing from about 3 to 12 percent of water are generally possessed of a pastelike consistency and are more conveniently loaded into accessible boreholes.

Compositions of the invention containing from about 12 to 25 percent of water are generally pumpable as a slurry and are useful in loading inaccessible or horizontal or upwardly sloping boreholes.

In preparing and detonating the composition of the invention, the ingredients of the composition are mixed together in small quantities as by kneading in a plastic bag or in larger quantities as with a mechanical agitator or paddle mixer. A

,load or charge of the so-prepared mixture is placed in the desired location, usually in the confinement of a borehole. A shaped charge such as a jet perforator containing a charge of RDX (cyclotrimethylene trinitramine) is placed next to the load armed with a suitable initiator for the shaped charge, such as a No. 8 Electric Blasting Cap. The shaped charge is oriented with respect to the explosive load so that the firing axis is directed toward the load, preferably its midpoint. The electrical lead from the blasting cap is rigged to a time-controlled firing mechanism or run to a remote control device and, if desired, a sand or gravel tamp is placed over the load and initiator. The load is then fired upon setting off the blasting cap and shaped charge.

The composition of the invention prepared and detonated as described is especially advantageously used in mining operations in which the use of low-cost compositions combining the properties of good heave or work potential with lower range brisance and low toxicity is to be desired.

To demonstrate the properties of the ammonium explosive mixture of the invention, various embodiments of the invention were prepared and tested. in each test a or a 25 pound quantity of explosive mixture was formulated of a particulated fertilizer grade ammonium nitrate and water, with or without particulated aluminum metal, in the proportions and amounts shown in the table. The individual proportions were in each case mixed in a separate polyethylene plastic bag of sufficient ticles passed a 20-mesh sieve and 85 percent by weight were retained on a lOO-mesh sieve. The aluminum metal was in the form of atomized pellets. The particle size of the particulated aluminum was such that about 0.4 percent was retained on a -mesh sieve, about 85 percent was retained on 200-mesh sieve and about 0.9 percent passed a 325-mesh sieve.

The prepared mixtures were loaded into individual shallow boreholes drilled in clay soil and having a diameter of 4 inches and a depth of about 4 feet. Successive boreholes were spaced about 20 feet apart. The loading of each hole was accomplished by first placing an initiator in the form of a shaped charge armed with a blasting cap in the bottom of the hole and running the lead wires of the blasting cap to a firing control switch. Each shaped charge was used and positioned with the jet end or firing axis facing upwardly.

The explosive mixtures contained in the plastic bags in which they were mixed were placed in respective test holes, the bag in each case deforming so as to cover the initiator. Sand was used as a tamp, the hole being filled from the bag to ground level with sand. Detonation of the mixture was attempted by closing the firing switch thus setting off the initiator at the bottom of the hole. In comparison test in the form of a blank, one hole was loaded solely with a 10 pound quantity of fertilizer grade of ammonium nitrate and an initiator.

The magnitudes of the detonations obtained were determined by measuring the size of the crater produced. While the crater size alone is not indication of the amount of earth formation that is broken up or loosened, it does give and indication of the work potential of the mixture detonated. The crater size herein reported shows how much material was thrown sufficiently so as not to fall back over the test hole. Test conditions and results are summarized in the table 2.

In order to compare the composition of the invention with conventional explosives varied amounts of percent dynamite each with a No. 8 Electric Blasting Cap therefor were placed in shallow test holes 4 feet deep, tamped with sand and detonated. Five pounds of dynamite so-loaded and detonated produced a crater 5 feet in diameter and L5 feet deep; 10 pounds of dynamite produced a crater 8 feet in diameter and 1 foot deep; while 25 pounds of dynamite produced a crater ll feet in diameter and 5 feet deep. The results of the blank, test No. 15, show the ammonium nitrate alone is not detonable under these conditions.

TABLE .2

indicator Wciuhtol Crntr'r BlnstltDX in rllttwnslmls. [wt Composition, percent Weight ing Silllllt'tl of load, cnp chnrgv. I ium- FGAN 11 0 Al pounds No. ounr-v ([(l' Depth Test N0.:

1 4 4 U7 3 .A 10 X 3. 25 10 Ii 10 a 3. 2n 85 7. 5 T. 5 1O 8 3. .5 6 4. 5 15 15 10 X 3. 25 I) 3 10 10 10 8 3. 25 5 1. 5 55 15 30 ll) 8 3. 15 H 3 6D 25 15 10 S 3. .35 H 4 87 3 1O .25 X l 12 3 5 10 25 8 l 12 3 80 10 I0 .25 8 1 l2 3 S10 5 5 l0 8 3. 25 l0 4 75 5 20 10 K 3. 135 10 ii 7 3 27 10 H 3. .25 10 5 60 5 35 10 8 3. .15 l() (i 10 8 1.75. 1 Ilcavcd and cracked 3 test. B 'lanlp only. NOTE.F GAN Fertilizer grade of ammonium nitrate; R l )X 'Irimotliylonv trlnitramino.

size to readily hold the quantity prepared. The various comln an additional test an explosive load weighing about 4 ponents of the mixture were weighed into the bag, the bag 70 pounds and having the composition 50 percent of ammonium closed and the contents mixed together by kneading the bag with the hands. The fertilizer grade ammonium nitrate contained about 0.7 percent of wax, 1 percent of diatomaceous earth and 0.3 percent of chalk. The particle size of the arrimonium nitrate was such that 94 percent by weight of the parnitrate, 20 percent of water, and 30 percent of particulated aluminum was used to fill a 3 inch by 12 inch steel pipe nipple which was capped on both ends and laid on the ground. The load was initiated by a shaped charge, containing 3.25 ounces 75 of RDX, which was positioned at one end of the pipe nipple so as to fire longitudinally into the pipe nipple. The resulting detonation destroyed the pipe nipple.

The compositions of the invention possess the additional advantage that they are little affected by a moist environment and can even tolerate a moderate amount of connate water.

What is claimed is:

1. An explosive composition comprising a particulate ammonium nitrate phase, an aqueous solution phase substantially saturated with respect to ammonium nitrate and at least one particulate metal, the metal particles ranging in size such that a substantial proportion of the particles are larger than those passing about a 325-mesh sieve.

2. The composition of claim 1 wherein a substantial portion of the particulate metal is of a size smaller than that retained on about a 20-mesh sieve.

3. The composition of claim 1 including in addition a thickening agent dispersed therein.

4. The composition of claim 1 wherein the particulate metal ranges in size such that about 85 percent of the particles are retained on a l40-mesh sieve and not more than about l per cent pass a ZOO-mesh sieve and comprises up to about 35 percent by weight of the composition.

5. The composition of claim 1 wherein the particulate metal is a light metal.

6. The composition of claim 1 wherein the particulate metal is a light metal selected from the group consisting of magnesium, magnesium-base alloys, aluminum and aluminum-base alloys.

7. The composition of claim 1 wherein water ranges from about 3 to about 25 percent by weight of the composition.

8. The composition of claim 1 including in addition an additional inorganic salt containing nitrogen.

9. The composition of claim 1 including a thickening agent in an amount ranging from about 0.1 to about 5 percent by weight based on the weight of the aqueous phase.

10. The composition of claim 9 wherein the thickening agent comprises at least one material selected from the group consisting of methyl cellulose, gum karaya, carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu natural, lrish moss, Iceland moss, or high molecular weight polyacrylamide.

11. The composition of claim 1 including in addition at least one inorganic salt selected from the group consisting of potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chlorate, potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate, or ammonium hypophosphite.

12. The composition of claim 1 wherein the particulate metal is a light metal and comprises up to about 35 percent by weight of the composition.

13. The composition of claim 1 wherein the particulate metal comprises up to about 35 percent by weight of the composition.

14. An explosive composition comprising:

a. from at least about 40 percent of ammonium nitrate at least a portion of which is in particulate form;

b. from 3 to about 25 percent by water, substantially saturated with ammonium nitrate;

c. up to about 35 percent of a particulate light metal the particles ranging in size such that a substantial proportion of the particles are retained on about a 325-mesh sieve; and

d. a thickening agent.

15. The composition of claim 14 including in addition up to about 35 percent of an additional inorganic salt containing nitrogen and having whichever is the lower of the melting and decomposition temperature greater than about C.

16. The composition of claim 14 wherein the particulate metal is selected from the group consisting of magnesium,

magnesium-base alloys, aluminum and aluminum-base alloys.

III t I i 1! 

2. The composition of claim 1 wherein a substantial portion of the particulate metal is of a size smaller than that retained on about a 20-mesh sieve.
 3. The composition of claim 1 including in addition a thickening agent dispersed therein.
 4. The composition of claim 1 wherein the particulate metal ranges in size such that about 85 percent of the particles are retained on a 140-mesh sieve and not more than about 1 percent pass a 200-mesh sieve and comprises up to about 35 percent by weight of the composition.
 5. The composition of claim 1 wherein the particulate metal is a light metal.
 6. The composition of claim 1 wherein the particulate metal is a light metal selected from the group consisting of magnesium, magnesium-base alloys, aluminum and aluminum-base alloys.
 7. The composition of claim 1 wherein water ranges from about 3 to about 25 percent by weight of the composition.
 8. The composition of claim 1 including in addition an additional inorganic salt containing nitrogen.
 9. The composition of claim 1 including a thickening agent in an amount ranging from about 0.1 to about 5 percent by weight based on the weight of the aqueous phase.
 10. The composition of claim 9 wherein the thickening agent comprises at least one material selected from the group consisting of methyl cellulose, gum karaya, carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust bean gum, balsam tolu natural, Irish moss, Iceland moss, or high molecular weight polyacrylamide.
 11. The composition of claim 1 including in addition at least one inorganic salt selected from the group consisting of potassium nitrate, sodium nitroprusside, potassium ferrocyanide, ammonium chlorate, potassium nitrate, strontium nitrate, sodium cyanide, calcium nitrate, or ammonium hypophosphite.
 12. The composition of claim 1 wherein the particulate metal is a light metal and comprises up to about 35 percent by weight of the composition.
 13. The composition of claim 1 wherein the particulate metal comprises up to about 35 percent by weight of the composition.
 14. An explosive composition comprising: a. from at least about 40 percent of ammonium nitrate at least a portion of which is in particulate form; b. from 3 to about 25 percent by water, substantially saturated with ammonium nitrate; c. up to about 35 percent of a particulate light metal the particles ranging in size such that a substantial proportion of the particles are retained on about a 325-mesh sieve; and d. a thickening agent.
 15. The composition of claim 14 including in addition up to about 35 percent of an additional inorganic salt containing nitrogen and having whichever is the lower of the melting and decomposition temperature greater than about 100* C.
 16. The composition of claim 14 wherein the particulate metal is selected from the group consisting of magnesium, magnesium-base alloys, aluminum and aluminum-base alloys. 